1. Field of the Invention
The present invention relates to a separation conveyance device, an image forming apparatus, a method for controlling the separation conveyance device, and a computer-readable recording medium.
2. Description of the Related Art
Image forming apparatuses such as printers and multifunction printers and image reading apparatuses such as scanners separate a sheet from stacked sheets and convey the separated sheet using feeding mechanisms or automatic document feeders (ADFs), for example. Sheet separation mechanisms used in such image forming apparatuses and image reading apparatuses are required to prevent the occurrences of non-feeding in which a sheet fails to be fed, overlapped feeding in which multiple sheets are fed while being overlapped, and delay of a sheet separation time, for example. The delay of a sheet separation time leads to a reduction of productivity of the apparatus, for example.
In recent years, detection of the leading edge of a sheet using an optical sensor and determination of a conveyance state of the sheet on the basis of the detection result have been generally performed. Japanese Laid-open Patent Publication No. 2011-084399 discloses a technique in which a passage time between the leading and the rear edges of a sheet is measured on the basis of a detection result by an optical sensor and an error in sheet separation is determined on the basis of the measurement result.
Another technique is known in which the thickness of a sheet is measured by an overlapped feeding detection sensor using ultrasonic waves and it is determined whether or not the conveyed sheet is in a tendency of overlapped feeding.
Conventionally, the leading edge detection for determination of a conveyance state has been performed using an optical sensor used for sheet registration. In an image forming apparatus, a process for image forming starts just after the sheet registration, for example. This process, thus, causes a problem in that even if an error in sheet separation is detected the sheet may be conveyed so as to be subjected to image forming while being in the error state. To solve such a problem, an optical sensor may be additionally provided for detecting the conveyance state ahead of the position where the sheet registration is performed in the manner as disclosed in Japanese Laid-open Patent Publication No. 2011-084399. This, however, increases the cost of the apparatus.
The technique employing the overlapped feeding detection sensor using ultrasonic waves has a problem in that it is difficult for the technique to be applied to a sheet with an unknown thickness because the determination is performed on the basis of the measurement result of the thickness of the sheet. In addition, the overlapped feeding detection sensor increases the cost of the apparatus.
In view of such problems, there is a need to enable the conveyance state of a separated and conveyed sheet to be detected using a simpler structure.